Various possible uses of brake devices are known in the case of which a holding function of the brake device is desired, that is to say in which, once a brake pressure has been demanded at the brake actuators by the driver by way of the brake pedal, said brake pressure should be held.
For example, in the case of a vehicle with automatic transmission, the vehicle must be held at a standstill by the driver by way of the brake pedal for as long as a drive stage is engaged, because the vehicle otherwise tends to move forward slowly.
Furthermore, in the case of a vehicle with a manual gearbox, complex interaction, which must be initiated by the driver, between handbrake, clutch and accelerator pedal is necessary in order to start off on a gradient.
In particular in the case of transport vehicles, such as for example refuse collection vehicles, or public service buses, it is furthermore the case that frequent stopping of the vehicle for short limited time durations is desired, during which, in the case of transport vehicles, the vehicle is loaded or, in the case of public service buses, passengers embark and disembark. During the holding time, the vehicle driver must continuously hold the brake pedal with the desired braking force, or must even increase the braking force if the vehicle, standing on a gradient, begins to roll in a backward direction owing to an increase in weight, for example as a result of loading.
According to the prior art, therefore, holding systems are known which maintain a brake pressure demanded by the driver by way of actuation of the brake pedal, and which, for this purpose, utilize the pressure control valves of an existing anti-lock system (ABS). If the brake pressure at the brake actuators is to be held, the pressure control valves of the ABS are closed, such that the pressure prevailing at the brake actuators continues to prevail even after the brake pedal has been released.
Such systems are however only suitable for ensuring a holding function or pressure-holding function for a limited time, because the valves permit a small fluid flow even in the closed state, and thus the pressure to be held rapidly decreases again. Furthermore, the valves are not suitable for increasing the pressure prevailing at the brake actuators. Further modifications to the brake device or brake system, in particular by way of the addition of additional pressure lines and multiple valves, are necessary for this purpose.